1) Field of the Invention
This invention relates generally to fabrication of a semiconductor device and more particularly to a method for minimizing copper diffusion into a plasma enhance chemical vapor deposition inorganic dielectric layer by doping the inorganic dielectric layer with phosphorous (P), or sulfur (S), or both.
2) Description of the Prior Art
As semiconductor dimensions continue to shrink and performance requirements continue to increase, it has become desirable to use copper for interconnections. However, traditional plasma enhanced chemical vapor deposition (PECVD) oxide (SiO.sub.2) dielectric layers suffer from copper migration into the oxide from the interconnect. To prevent this copper migration barrier layers (typically tantalum or tantalum nitride) are deposited onto the sidewalls of contact (via) openings in the dielectric layer, prior to depositing the copper.
As the openings continue to shrink, however, a barrier layer can cause performance problems. The barrier layer can adversely affect RC delay degrading device performance. Coverage of trenches and/or vias by a barrier layer is not uniform. THe barrier layer is thinnest along the side and at the bottom corners of trenches and/or vias, thereby offering poor barrier properties. Also, the crystalline nature of barrier metals tend to allow diffusion of copper along the grain boundaries.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,654,232 (Gardner) shows a method for forming a copper interconnect using a silicon nitride or tantalum wetting layer and a copper reflow process to eliminate voids. Gardner does suggest that the dielectric layer can be phosphorous doped silicon glass (PSG), however the dielectric layer is not in contact with the interconnect. Instead a silicon nitride or tantalum wetting layer is used to prevent copper diffusion. Therefore, Gardner does not suggest eliminating the barrier layer.
U.S. Pat. No. 5,739,590 (Sakamoto et al.) teaches a nitrided sulfur glass (NSG) and phosphorous doped silicon glass (PSG) interlayer insulating film (ILD). This invention does not disclose or suggest copper interconnects, nor does it address copper diffusion.
U.S. Pat. No. 5,451,542 (Ashby) teaches a sulfur surface passivation process.
U.S. Pat. No. 6,001,415 (Nogami et al.) and U.S. Pat. No. 5,985,762 (Geffken et al.) show copper interconnect processes with copper diffusion limited by depositing a barrier layer on the sidewall of an insulating layer prior to depositing copper.